Tegan Jovanka held possession of a TARDIS key, given to her by the Fifth Doctor. (AUDIO: Hexagora)
Early in her travels with the Doctor, Tegan did not have a TARDIS key. When the TARDIS landed on Monarch's ship, she was given the Doctor's spare key in the event she was separated from the group. (TV: Four to Doomsday)
She did not have a key when Kamelion began travelling in the TARDIS. (AUDIO: Devil in the Mist)